Television scanning apparatus



Oct. 17, 1939. F. SCHROTER 2,176,190

TELEVISION SCANNING APPARATUS Filed Sept. 14, 1956 INVENTOR FR/TZ SGHROTER ATTORNEY Patented 17, 1939 'rnmvrsrou some APPARATUS rm; Schroter, Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. 1]., Berlin,- Germany, a corporation of Germany Application September 14. 1930, Serial No. 100,609

Germany August 14, 1935 3 Claims. (Cl. ire-7.2)

This invention relates broadly to cathode ray type television scanners with improvements for eliminating to a wide extent the electrical and structural limitations and dimcultles of the present mown cathode ray type scanning apparatus.

The invention relates more particularly to a cathode ray tube type of scanning apparatus in which an electron image is formed of the object to he sced, which image is stored for a period of time, and is then released by a cathode ray arrangement which operates in a gas-filled medium.

In the present mown cathode ray type of television scanners, which store an optical image, the .cathode ray is moved across a storing grid screen and the cathode ray itself performs a switching function for the purpose of converting the stored .charge or electricity into potential difierences 'wlnch sequentially are amplified and transmitted. This switching function, cages it is commonly termed, recharging functinn, takes place across an electrical path between the anode of the tube and the aforementioned screen element and hence there is a considerable inner resistance to the iiow of secondary emission from the storing means. Since the time constant of the charge transferred is limited to a low value (of the order oi one millionth of a second) owing to the great nher of screen elements to be scanned for scanning a complete individual image, it is necessary to employ very low capacities in the charged storing device. It is therefore the object of this invention to eliminate to a wide extent the electrical and structural limitations and difiiculties existing under these conditions.

According to this invention, a separate gaseous space is provided in which the cathode ray which discharges the stored device is produced and controlled for eifecting scanning in lieu of the present known arrangements in which the scanning is carried out in a high vacuum space. The gas pressure may be, for instance, of the order of 11H.

1 first provide photo-electric means which are adapted to form an electron image of the optical image which is projected thereon and this optical image is transferred in a vacuum to the electron storage means which may correspond to either a single line of the electron image or the complete image, that is to say, the electron image is stored either as a complete image or elemental width strips or sequentially stored and individually scanned. The electron storing device is adapted to act as a com wall in the tube thus forming a. gas tight arrangement between the section of the tube inwhich the electron image is developed and which is evacuated, and the section of the tube in which the cathode ray beam is developed and which is filled with a gas of a transfer in the neighborhood of 10" mm. of course, the efiect of msuflicient tightness could be eliminated by arranging in the electron image compartment absorption means for any gas that might leak into the compartment or by subjecting this space continuously to the action of a suction pump. In the compartment where the oathode ray beam is developed, the gas then would obviously have to be replaced and accordingly a control storage container might furnish this gas at the proper pressure. The charges released by the electron image may be transferred through the separa-- wall into the scanning space or compartment where they can he evaluated. Oh=

viously, of course, electrodes which are insulated against each other have a common counterlayer placed opposite their tube. is known in the art.

Such an arrangement according to the inven tion can be constructed in the simplest manner in the form of a single image line of grid screen electrodes. The electron main of the image space is then caused to act upon the row of individual cells line after line by means of a magnetic or electrical deviation held. In order to thereby multiply the variation of the charge produced by the impinging image electrons, the surfaces impinged are activated with substances favoring secondary emission preferably by means of highly electro-positive layers of known type. Where multiplication is to be obtained the factor of secondary emission must be greater than 2. The individual insulated cell electrodes are suitably inserted through a glass layer by the use of enamel glass or the like having a low melting point, and terminate in the gaseous cathode ray scan- ,ning space.

would lead in a high-vacuum space to a space charge produced in front of the screen element scanned. As a result thereof the inner resistance of the discharge path would again be increased in an undesirable manner. The operation in a gaseous space avoids this drawback, in that the space charge action of the electrons will be compensated by the positive gas ions tamed by the cathode ray. Hence a very low discharge resisttion is illustrated in the drawing. Herein l is the object to be transmitted by television, 2 is an objective which recreates through the lightpermeable front wall of the image analyzing tube 4 the object on the transparent photo-electric layer 3. The magnetic focussing coil 5 energized by D. C. projects the electron image emitted by 3 into the plane of the cell screen 9. 6 designates the magnetic field whose purpose is to move by means of a saw tooth-shaped exciter current the electron beam from line to line across the row of cells 9. I is the acceleration anode of ring shape for the image electrons emitted by 3. The individual cells 8 are passed through the separation wall 8 by the use of insulating through guides. The common countercapacity of these individual capacitive electrodes is indicated by the dash lines by which the through lead I II of the countercapacity within the separating layer 8 is continued. In the scanning space an electrode net H may be provided to serve as absorption anode for the charges liberated by the cathode ray, and whose potential regulates at the same time the velocity of the ray. The cathode ray is indicated by the dash line I 8, and it moves across the row of the cell screen 9 under the action of a potential field of saw-tooth form applied between the deviation plates l3, I4 the conducting end surfaces of said row of the cell screen being in contact with the gas content of the scanning space. I2 is an auxiliary anode, i5 is the first anode through whose central orifice the gas concentrated ray l8 passes, it designates a Wehnelts cylinder of known type, I I is the point-shaped ray cathode. In the space at the right oi the separating layer 8 by the aid of the means stated for concentrating the cathode ray l8 and at the same time for eliminating the space charge at the screen elements, the most favorable gas pressure is maintained. The space for the image in electrons at the left of 8 must however be highly evacuated.

What I claim is:

1; A- television scanning apparatus comprising a cathode ray tube which includes an envelope divided into a. plurality of substantially gas tight compartments, one of said compartments being highly evacuated and containing means for developing an electron image of the object to be scanned, electron storage means adapted to not as a compartment wall in said envelope, means for superimposing the electron image on said electron storage means, means for developing a cathode ray beam in the compartment or the en-- velope containing gas at a low pressure remote from the compartment in which the electron image is developed, and means comprising the cathode ray beam, an electrode, and a gas for discharging said storage means sequentially with the cathode ray.

2. A television scanning apparatus comprising a cathode ray tube which includes an envelope divided into a plurality of substantially gas tight compartments, one of said compartments being highly evacuated and containing means for developing an electron image of the object to be scanned, electron storage means adapted to act as a compartment wall in said envelope, means for developing a cathode ray beam in a compartment oi the envelope containing gas at a low pressure remote from the compartment in which the electron image is developed, an electrode in said gas filled compartment closely associated with said electron storage means, and means comprising said cathode ray, an electrode, and a gas for discharging said storage means sequentially with the cathode ray.

3. Apparatus according to claim 1 characterized in that the gas filled compartment is maintained at a pressure of 10- mm.

FRITZ SCHROTER. 

